Constant-temperature oven



July 10, 92s. 1,676,876

W. H. STANNARD CONSTANT TEMPERATURE OVEN Filed Nov. 30, 1925 2Sheets-Shet 1 MLLnesscs 50 15 53 1) hwafl Z! 2/1 [aid Siam/(MY! I M July10, 1928.

W. H. STAN NARD CONSTANT TEMPERATURE OVEN 2 Sheets-Sheet Inventor mafia53 M 'ulv'dinesses Hu s Patented July 10, 1928.

UNITED. STATES 6,81 PATENT OFFICE,

-WINFIELD H. STANNARD, OF MATTESON, ILLINOIS, ASSIGNOR TO CENTRALSCIENTIFIC ,COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS. v

CON STAN IE-TEMPERATURE OVEN.

This invention relates to ovens for at ministering treatment at constanttemperatures and has for its principal objects to provide a greateruniformity of temperature throughout the difierent parts of the oven anda greater time-constancy of temperature of the oven as a whole. Morespecific ob jects will appear and be best understood as the disclosureproceeds and the description is read in connection with the accompanyingdrawings illustrating the preferred embodiment of the invention, inwhich Fig. 1 is a vertical section through the oven; Fig. 2 is atransverse section thereof;

Fig. 3 is a perspective view of a unit including the preferredelectrical equipment for the oven;

Fig. 4 is a plan view of the panel arrangement, and i I Fig. 5 is awiring diagram illustrating the most advantageous connection of theapparatus.

The most satisfactory oven enclosure for general application includes abottom 10 and a top 11 connected by sides 12 and 13, a back 14 and afront 15. Each of these is so fab ricated of suitable materials as to beas nearly non-conducting as practicable. For example, each part of theenclosure may consist of an outer sheet of asbestos board 16, spacedfrom an inner sheet of like board 17, by a filling of asbestos fiber,mineral wool, or the like 18. I 5 The front 15 is shown as a door,hinged at 19, and having beveled edges 20m make a close joint withcorrespondin edges21 on the facings 22 attached to the sides 12 and 13.For the best results the electric heating 5 element should consist of apluralit of units presenting uniform wattage throng out their en'gth;For example, the units may be coils 23 extending around the lowerportion of the container and supported in notched blocks 5 of asbestosboard 24, secured to a base 25 of asbestos board, or other material,that will not reflect or radiate heat to a great extent.

Extending upwardly from the heating element is a flue, or flues, 26, inopen communi- 3 cation with the enclosure at both ends." In

the simple construction shown, a wall 27 extends across the enclosurespaced a short distance from the back 14 and terminating just above "theblocks 24 at the bottom 10, and

5 about the same distance 'fromtheto'p'11.

adjustments in opening and closing the inner Secured to this wall andextending parallel to the sides of the corresponding facings, are

walls 28 and 29, which terminate short of the door 15 and are supportedby brackets 30.

A wall 31, of glass, normally rests against the front edges of the walls28 and 29 and is supported by springs 32 on a door r'ame 33, which isfitted with a second glass wall 34 in spaced relation to the wall 31.The door frame 33 is hinged to one facing 34 and closes against anopposed facing 35 secured. respectively to the sides 12 and 13. Thesprings 32 serve to hold the glass wall 31 in proper relation and permitit to make slight door. The walls 28 and 29 are equipped with supportsfor shelves 36.

The side 13 is cut away adjacent to the bottom to form an elongatedopening 37 through which the base 25 with the heating element thereon,may he [slid in inserting that element into or withdrawing it from thecontainer. Attachedto the base'25 is a block 38 of insulating material,.s uch as transite, and to this, in turn, is attached a panel 39, adaptedto carry various instruments and the wiring. The outer casing of thewall 13 is madein two pieces overlapped, as indicated at 40 to providespace 41 inwardly with respect to the panel, for the connections to thevarious instruments. This wall is also perforated at 42 to admit thethermoregulator 43, which is preferably of the t e set forth in thepatent to de Khotinsky, 0. 1,375,780 of April 26, 1921.

In addition to the thermoregulator, the panel carries a connecting plug44, a switch 45. a pilot lamp 46 and condensers 47.

Referring to the wiring diagram in Fig. 5, it will be seen that thecoils 23 are ar ranged as separate units connected in parallel acrossthe line 48. a

The best results are obtained when these units are all'the same wattageand two of the units are controlled by the thermoregulator throughseparate contacts 49 and 50. "The bottom 10 is provided'with inletpassages 51 and the top with a vent 52.

Operation: When current is supplied to the heating element, air directlyin contact withthe coilsbecomes heated and rises. 'In its upwardmovement it entrains, or otherwise carries along other air. Thusconvection currents are establishedwhich pass upwardly through the fiuesthen inwardly and no downwardly through the enclosure between the fluewalls, and outwardly through and around the coils and upwardly againthrough the flues. During the upward movement the highly heated air andthe air carried with it become mixed until the product at the top of theflues is practically uniform in temperature. This flows inwardly anddownwardly over the material to be treated and thus establishesthroughout the space between the flue walls a zone of practicallyuniform temperature.

Placing the walls 27, 28, 29 and 31, inwardly with respect .to thecoils, not only 5 insures that the heated air will immediately pass intothe fines, but results in shielding the test material near the top ofthe oven from heat radiated directly from the coils while allowing suchradiated heat to reach the test material near the bottom; thus theradiated heat reaches only that material that, were it heated byconvection currents only,

' would be cooler than material near the top.

Thus, the two sources of heat are so balanced that material near the topof the oven is at heating element substantially equal to two of theunregulated units the danger from changes in room temperature ispractically eliminated. Suppose the room temperature to be 71 F. atthebeginning of the treatment, the desired temperature in the oven 100 F.,the wattage in the two units 23 suflicient to raise the temperature 20.If only a single unit 23 was under the control of the thermoregulatorand the room temperature dropped 3 there would be a failure ofregulation. However, by having the regulated portions of the heatingelement of substantially the same watt-age as two units 23 it is alwayspossible to prevent either a drop or an increase in room temperaturefrom taking the desired temperature out of the range of control of theregulator.

By breaking the regulated portion into a plurality of units the damageto the contacts is greatly reduced.

The pilot lamp 46 connected as shown in Flg. 5, will be lighted when there lated units are in operation and'will be dar when the regulated unitsare cut out. To reduce the current through the lamp it may be connectedacross a suitable shunt 53.

I claim as my invention:

1. In a device of the class'described, the combination of an ovenenclosure, including abottom, a top and walls, a heating elementextending about the enclosure and located adjacent to the bottom, andthe walls, and a flue communicating at its bottom with the heatingelement and extending upwardly along the walls and delivering adjacentto t e to 2. Iii a device of the class described, the combination of anoven enclosure including a bottom, a top and walls connecting the bottomand top, inner walls spaced inwardly from the walls of the enclosure andforming with the first wall a flue surrounding the oven space, saidinner walls being cut away adjacent to the bottom and top, and a heatingelement adjacent to the bottom of the space between the outer and innerwalls, said flue communicating at its bottom with the heating element,and at its top with the oven space.

3. In a device of the class described, the combination of an ovenenclosure including a bottom and a top connected by side walls, anelectric heating element of uniform wattage arranged around the ovenadjacent to the bottom and the walls, and flue walls extending upwardlyinside of the heating element and defining with the side walls uprightflues havin open bottoms in communication with the eating elements.

4. In a device of the class described,"'the combination of an ovenenclosure includinga bottom and. top connected by walls having a door,flue walls spaced inwardly from the walls of the enclosure and includinga transparent door opposite to the first door.

5. Ina device of the class described, the combination of an ovenenclosure including a bottom and a top connected by front, back and sidewalls, one of said walls having a door permitting access to theenclosure, a flue within the enclosure including a transparent dooropposite to the door in the .wall of the enclosure.

6. In a device of the class described, the combination of an ovenenclosure includin a bottom and atop connected by front, bac and sidewalls one of said walls including a door and a flue connectin the lowerand upper portions of the enc osure adjacent to each of said walls.

7. In a device of the class described, the combination of an ovenenclosure including a bottom and a top connected by front, back and sidewalls, one of said walls having a 1 door, a flue within the enclosureincluding a plurality of transparent walls movable to and from aposition behind said door.

8. In a device of the class described, the combination of an ovenenclosure including a bottom and a top connected by walls, one of whichhas an opening adjacent to the bottom, a base movable through saidopening into and out of the enclosure and an electrical resistanceelement carried by the base and movable therewith through the opening.9. In a device of the class described, the combination of'an ovenenclosure including a bottom and a top connected by walls, one ofwhiclr-has an opening adjacent to the bottom-fan electrical resistanceelement, a base'lior said element movable through said opening into andout of the enclosure, and an instrument panel attached to the base andadapted to close said opening when the base is within the enclosure.

10. In a device of the class described, an electrical heating elementincluding several units, a plurality of which are of substantially equalwattage and a thermo-regulator controlling a portion only of said unitssub- 7 stantiallyequal in wattage to two of the units of equal wattage,the remaining heating units being permanently in circuit.

11. In a device of the class described, an electrical heating element,including a pinrality of units of substantially equal wattage, andthermo-regulating means controlling two of said units only, the'remaining heating units being permanently in circuit.

12. In a device of the class described, the combination of an ovenenclosure including a bottom, a top and Walls connecting the bottom andtop, inner walls spaced inwardly from the walls of the enclosure and cutaway adjacent to the bottom and top, and a .heating element looped aboutthe bottom of the enclosure between the inner and outer walls.

13. In a device of the class described, the combination of an ovenenclosure including abottom,-a top and walls connecting the bottom andtop, inner walls spaced inwardly from the walls of the enclosure ,andcut away adjacent to the bottom, the inner and enclosure walls definingfines having open bottoms, one of the enclosure walls. having an openingadjacent to the bottom, and an electrical resistance element extendingabout the bottom of the oven adjacent to the bottom of the inner wallsand being removable through said opening, said resistance being incommunication with the open bottoms of the fines.

In testimony whereof I aflix my signature.

WINFIELD H. STANNARD.

